Field of the Invention
The present invention relates to polyboronic compounds, compositions containing such compounds and methods of making and using the same.
Description of the Related Art
Hydraulic fracturing techniques are widely used to enhance oil and gas production from subterranean formations. During hydraulic fracturing, a fluid is injected into a well bore under high pressure. Once the natural reservoir fracture gradient is exceeded, the fracturing fluid initiates a fracture in the formation that generally continues to grow during pumping. The treatment design generally requires the fluid to reach a maximum viscosity as it enters the fracture that affects the fracture length and width. The viscosity of most fracturing fluids is generated from water-soluble polysaccharides, such as galactomannans or cellulose derivatives.
The gelled fluid can be accompanied by a propping agent (i.e., proppant) that results in placement of the proppant within the fracture that has been produced. The proppant remains in the produced fracture to prevent the complete closure of the fracture and to form a conductive channel extending from the well bore into the formation being treated once the fracturing fluid is recovered.
Guar based fracturing fluids are the most commonly used fluids in reservoir stimulation. Guar is composed of polymannose backbone with galactose branching with an approximate ratio of 2:1. The solubility of guar gum is greatly enhanced by the galactose branching compared to other polysaccharides.
Hydrated guar or its derivative (linear gel) at ambient temperature does not possess the required viscosity for proppant transport. Thus, crosslinkers, such as boron, zirconium, titanium compounds, are used to significantly improve viscosity of the fluid system. Hydrated guar gum is mostly crosslinked with borates while derivatized guar gums such as, carboxymethyl guar (CMG), hydroxypropyl guar (HPG) and carboxymethyl hydroxypropyl guar (CMHPG), are mostly crosslinked with transition metals. Borate crosslinked fluids are typically preferred due to their reversibility to mechanical shearing and favorable environmental properties.
Pumping fluids with high viscosity requires tremendous amount of horsepower due to high pipe friction, so delayed crosslinkers are desired. Further, while boron and zirconium crosslinking agents are effective for many types of fracturing fluids containing hydratable polymers, a certain amount of the polymer is needed to achieve the viscosity necessary to fractionate the formation. It is desirable to use as little polymer as possible in a fracturing fluid so that the overall cost of the fracturing job is lower. With reduced polymer loading, less polymer residue remains in the fracture and the sand pack after breaking. Formation damage is therefore minimized.
In view of the foregoing, a need exists for a crosslinking agent that would effectively increase the viscosity of the polymer, which also reduces the polymer loading as much as possible in fracturing fluids. In addition, a need exists for agents which are capable of exhibiting delayed crosslinking activity. A need also exists for compounds, such as polyboronic compounds, that can be prepared and have more than one B—N bond that helps with functions, such as crosslinking. Additionally, it would be advantageous if such crosslinking system is compatible with existing fracturing systems.